There has been proposed a developing device, which is detachably installed in an image forming apparatus such as a laser printer.
For example, JP-A-9-319202 describes a related art developing device including a unit frame having a partitioned developing chamber for receiving an auger roller, a supply roller, and a developing roller, and a toner cartridge detachably attached to the unit frame.
In the related art developing device, a toner supply port is formed at a central position (the central position in the axial direction of the developing roller) of the unit frame and the toner cartridge, and toner suction ports are formed at both sides of the toner supply port.
Toner stored in the toner cartridge is supplied from the toner supply port to an inside of the developing chamber. Thereafter, the toner is supplied to a supply roller, and then from the supply roller to the developing roller, and is carried on the developing roller. In contrast, the toner which has not been supplied to the supply roller is conveyed by the auger roller from the central position toward both end portions, and thereafter, the toner returns to the inside of the toner cartridge from the toner suction ports. Accordingly, the toner circulates and the flowability of the toner is secured.
However, when the toner supply port at the central position supplies toner from the toner cartridge to the inside of the developing chamber, and the toner suction ports at both sides return the toner from the developing chamber to the inside of the toner cartridge, in some cases the toner conveyed by the auger roller from the central position toward both end portions is not returned to the inside of the toner cartridge from the toner suction ports but is left accumulated at both sides within the developing chamber. In these cases, the toner accumulation may cause toner having different degrees of deterioration to become mixed within the developing chamber or the toner cartridge, thus deteriorating image quality.